1. Field of the Invention
The present invention relates to a magnetic material for high frequencies and, more particularly, to a magnetic composition of a calcium vanadium garnet system suitable for use in a range of high frequencies such as microwaves and millimeter-waves.
2. Description of the Prior Art
As a magnetic material for high frequencies, there have been used those such as manganese-magnesium ferrites, nickel-zinc ferrites, lithium ferrites and yttrium-iron-garnets (YIG), calcium-vanadium-garnets, etc. since they have a saturation magnetization (4 .pi.Ms) ranging from 500 to 4000 gauss. Among them, calcium-vanadium-garnets are known to be a magnetic material with a low magnetic loss which is given by a ferromagnetic resonance absorption half-line width (.DELTA.H). Thus, the calcium-vanadium-garnets make it possible to produce low-loss circuit elements such as isolators and circulators since they meet requirements for magnetic materials such that they must have not only a suitable value of 4 .pi.Ms but a small .DELTA.H.
Japanese patent publication No. 49-15754 (i.e., JP-B-49-15754) discloses a magnetic material for microwaves of a calcium-vanadium-garnet system in which a part of Ca is replaced with Y and a part of Fe is replaced with Sn to provide a composition expressed by the general formula: EQU (Ca.sub.3-y Y.sub.y)(Fe.sub.2-x Sn.sub.x)(Fe.sub.1.5+0.5x+0.5y V.sub.1.5-0.5x-0.5y)O.sub.12
where 0&lt;y.ltoreq.2.5, 0&lt;x.ltoreq.0.35y+0.3, and 0&lt;1.5-0.5x-0.5y. This material has a small saturation magnetization (4 .pi.ms), a small temperature coefficient of 4 .pi.Ms and small .DELTA.H.
In proceeding papers, p 424, of a lecture in a national meeting of the electronics-communications society for the 47 year of Showa, it has been reported by Takamizawa et al. that substitution of Y and Sn for parts of Ca and Fe causes a variation of 4 .pi.Ms, that a partial replacement of Fe with Sn lowers the anisotropic field and .DELTA.H.
However, such calcium-vanadium-garnet materials have a serious problem that a slight deviation of the composition causes considerable increase in both .DELTA.H and dielectric dissipation factor (tan .delta.) and interferes with the practical uses.
On the other hand, when the magnetic material is used for self-biasing phase converting elements or latching type phase shifters, it is required to have a large ratio of remanent magnetic flux density (Br) to maximum magnetic flux density (Bm), i.e., a large squareness ratio (Br/Bm), as well as small tan .delta.. However, the above calcium-vanadium-garnet materials cannot be applied to the phase converting elements since the greater Br/Bm, the greater is tan .delta., and the smaller the tan .delta. the smaller is Br/Bm.